Examples of HARM-structures include nanotubes (NTs) for example carbon nanotubes (CNTs), fullerene functionalized carbon nanotubes (FFCNTs), carbon nanobuds (CNBs), boron-nitride NTs (BNNTs), nanorods including carbon, phosphorous, boron, nitrogen and silicon containing nanorods, filaments and other tubular, rod, or ribbon or otherwise fibrous or high aspect ratio molecular structures (HARM-structures). HARM-structures are of great interest due to their unique and useful physical and chemical properties. For example, CNT based components have wide ranging applications including light-emitting diodes, transistors, filters, field emitters, photovoltaic devices and fuel cells.
Ideally, even an individual HARM-structure with a well defined property and in a specific location is sufficient for many applications. However, to date, manufacturing of structures based on individual HARM-structures has been too difficult, time-consuming and expensive to be commercially viable.
Consequently, for many purposes, thin films, sparse or dense networks or mats (heretofore referred to as networks) of HARM-structures are preferable, since networks can be easier to manipulate, assemble and integrate than individuals. The high conductivity of certain HARM-structures, such as metallic carbon nanotubes and carbon nanobuds, together with their extremely high aspect ratios allows for efficient electrical percolation, even in randomly oriented surface deposited mats or films. Networks of semi-conducting HARM-structures are useful, for instance, as the conductive channel of a transistor. Sparse networks or a mixture of metallic and semi-conducting HARM-structures can also be used as the conductive channel if the concentration of HARM-structures is sufficiently low so that there are no metallic pathways between the source and drain.
Random network CNT based devices have been already successfully used as gas detectors, transparent conductive coatings and field emitters. Also, they are considered to be strong candidates for ITO replacement in transparent electrodes where the high costs of raw materials and production processes together with performance barriers related to brittleness and coloring are limiting their commercial life-time.
Networks of CNT HARM-structures in polymer structures allow for the creation of flexible and transparent electronic devices. However, polymers cannot be used directly as growth substrates for, for example, carbon nanotubes due to the high temperatures often required for their synthesis. Therefore, several methods, such as dry printing and electrical or thermal precipitation have been proposed for transferring onto plastics.
Networks of CNT HARM-structures have previously been produced using e.g. filtration from a liquid, by depositing from a solution via spray coating or spin drying. Carbon nanotubes can also be suspended in solution and sprayed or spin coated onto e.g. silicon wafers, however, such techniques require additional processing steps and equipment.
Problems with prior art methods are the difficulty in patterning, the need to deposit on a desired substrate immediately, the need to put in solution and thus disperse, sonicate and functionalize HARM-structures before use, all of which can degrade the product and lead to complex and expensive manufacturing processes.